The present invention relates to arrangements for refilling the medication reservoir of an implanted medication infusion device, and, more particularly, to a disposable unit for refilling an infusion device of the type having means for maintaining the medication reservoir at a pressure substantially less than the pressure of the body in which the device is implanted.
Various types of implantable medication infusion devices have been heretofore proposed as shown, for example, in Haerten et al U.S. Pat. No. 4,077,405, Franetzki et al. U.S. Pat. No. 4,191,181, Portner et al. U.S. Pat. No. 4,265,241, Ellinwood U.S. Pat. No. 3,692,027, Tucker et al. U.S. Pat. No. 3,951,147, and Blackshear et al U.S. Pat. No. 3,731,681. In general, the refilling of the medication reservoir of such devices after they have been implanted in the body is accomplished by a conventional hypodermic needle and syringe, as shown in Haerten et al U.S. Pat. No. 4,077,405. Also, the arrangement shown in Sampson U.S. Pat. No. 4,190,048 may be employed to refill such devices.
In Franetzki U.S. Pat. No. 4,191,181, and in my copending application Ser. No. 554,197 filed Nov. 22, 1983, the implanted device is provided with means for maintaining the medication reservoir at a pressure substantially less than the pressure in the body in which the device is implanted. Such a negative pressure device can be refilled using a conventional hypodermic needle and piston syringe by simply letting the natural pressure differential from the ambient to the negative pressure reservoir pull the medication out of the syringe and into the implanted device. With such an arrangement the natural pressure differential may not be sufficient at high altitude to overcome the friction in the seals of the piston syringe. Also, the danger is always present that the piston could be inadvertently pushed and produce a pressure above body pressure which could accidently infuse a potentially lethal dose of medication into the patient's body if the needle of the external refill device does not initially engage the septum of the implanted device properly or becomes disengaged (due to motion of the patient or other reasons) before the refill is finished. Furthermore, the conventional hypodermic needle and piston syringe is not airtight and if used in a negative pressure type of implanted device presents a problem due to the fact that the tiniest bit of air leaking through the piston syringe will be immediately sucked into the reservoir. This is particularly undesirable in negative pressure type implanted devices which employ a pulsatle pump to infuse medication into the body, such as described in my above-identified copending application Ser. No. 554,197 which are quite sensitive to the presence of air in the medication reservoir. Extreme care must be exercised during the refilling operation to be sure that air bubbles are not introduced into the reservoir along with the desired medication. The requirement that the medication introduced into the reservoir be free of air bubbles is in addition to the further requirements that the conditions under which the medication is introduced are intrinisically safe with respect to avoiding accidental gross infusion of medication into the patient and maintaining sterility of the medication during the refill process.